Add more multisigner tests

A zone in multisigner model 2 should also be possible to publish the
CDS and CDNSKEY records from their KSK into the zone operated by the
other provider.

bin/tests/system/multisigner/clean.sh

@@ -14,6 +14,8 @@
 set -e
 
 rm -f *.created
+rm -f cdnskey.ns*
+rm -f cds.ns*
 rm -f created.key-*
 rm -f dig.out.*
 rm -f python.out.*